1. Field of the Invention
The present invention relates to a carbon nanotube, a supported catalyst including the same, and a fuel cell using the supported catalyst.
2. Description of the Related Art
Fuel cells are energy conversion devices that transform energy stored in a fuel into electricity through electrochemical reactions between the fuel and an oxidative gas. Fuel cells can be classified into solid oxide electrolyte fuel cells using a solid oxide electrolyte, which can operate at 1000° C., molten carbonate salt fuel cells, which can operate at 500-700° C.; phosphoric acid electrolyte fuel cells, which can operate at about 200° C.; and alkaline electrolyte fuel cells and solid polymer electrolyte fuel cells, which can be operate at an ambient temperature or at a temperature of about 100° C. or less.
Examples of solid electrolyte fuel cells include proton-exchange membrane fuel cells (PEMFCs) utilizing hydrogen gas as a fuel source, direct methanol fuel cells (DMFCs) which generate power using a liquid methanol solution directly supplied to an anode as a fuel source, and the like. Polymer electrolyte fuel cells are clean energy sources, can replace fossil fuels, and have high power density and high energy conversion efficiency. In addition, polymer electrolyte fuel cells can operate at an ambient temperature, and can be miniaturized and sealed. These characteristics make polymer electrolyte fuel cells a desirable choice for pollution-free vehicles, power generating systems for home use, portable telecommunications equipment, military equipment, medical equipment, space technology equipment, and the like.
PEMFCs produce a direct current through an electrochemical reaction between hydrogen and oxygen, and contain a proton-exchange membrane interposed between an anode and a cathode.
The proton-exchange membrane is formed of a solid polymer material, such as NAFION™, that has good proton conducting properties and allows minimal cross-over of unreacted gas or fuel to the cathode portion. The anode and the cathode include backing layers for supplying reaction gases or a liquid, and a catalyst for the oxidation/reduction of the reaction gases.
As a hydrogen reaction gas is supplied to the PEMFC, hydrogen molecules are decomposed into protons and electrons through an oxidation reaction in the anode. The protons permeate across the proton-exchange membrane to the cathode.
Meanwhile, oxygen is supplied to the cathode, and the oxygen accepts electrons to form oxygen ions. The oxygen ions then combine with the protons from the anode to produce water.
A gas diffusion layer (GDL) in the PEMFC is included in each of the anode and the cathode. A catalyst layer that promotes the fuel cell chemical reactions is formed on each the anode and cathode backing layers. The anode and cathode backing layers can be formed of carbon cloth or carbon paper.
DMFCs have a similar structure to PEMFCs described above, but use a liquid methanol solution instead of hydrogen as a fuel source. As a methanol solution is supplied to the anode, an oxidation reaction occurs in the presence of a catalyst to generate protons, electrons, and carbon dioxide. Although DMFCs exhibit somewhat lower energy efficiency than PEMFCs, the use of a liquid fuel in DMFCs makes the application of DMFCs to portable electronic devices easier.